Lecture-notes on chemistry for dental students / by H. Carlton Smith.

  • Smith, H. Carlton (Henry Carlton), 1866-
Date:
1912
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Licence: Public Domain Mark

Credit: Lecture-notes on chemistry for dental students / by H. Carlton Smith. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

    63/444 (page 47)
    The soluble chromic salts most easily obtained are chrome alum, KCr(504)2, chromic sulphate, Cr2(804)3, and chromic chlorid, CrClg. With a 5% solution of either of these the fol- lowing may be demonstrated: Cr2(SO)3 with (NH4)2S gives greenish precipitate of Cr(0H)3. Similarly to Al, the chromium hydroxid is precipitated by the alkaline carbonates and the alkaline sulphids as well as by the hydroxids; and then by boihng the Cr(0H)3 with NaOH or KOH, or by fusing with Na2C03 and KNO3, chromates of the alkalis are produced. The sohd dichromate K2Cr207 with strong H2SO4 gives, in the presence of chlorids, the reddish-brown gas Cr02C]2 (chloro- chromic anhydrid or chromium dioxychlorid) used as a test for chlorids (page 90). Analysis of Group III. (Fe, Al, Cr. Phosphates and oxalates being absent.) The filtrate from Group II must be freed from H2S by boil- ing with a few drops of HNO3 in a porcelain dish till a drop removed by a glass rod does not blacken filter-paper wet with a solution of lead acetate. This treatment also serves to oxidize the iron (reduced by H^S) to ferric salt and at the same time concentrates the solution. To the clear solution thus obtained add 10 c.c. of NH4CI solution, then NH4OH till alkaline, when the metals of this group will separate out as hydroxids: Fe(0H)3 brick-red, A1(0H)3 white, Cr(0H)3 bluish-green. Filter, Wash carefully, and dry precipitates, removing paper from funnel. Group III. Groups IV, V, and VI.